Electrical fuses for projectile or the like



Jan. 3, 1967 I LOHNERT v r 3,295,449

ELECTRICAL FUSES FOR PROJECTILE OR THE LIKE Filed Oct. 9, 1964 i 5 Sheets-Sheet 1 O INVENTOR ADALBERT LUHNERT Jan. 3, 1967 A HNER+ f saw-1,449

ELECTRICAL FUSES FOR PROJECTILE OR THE LIKE Filed Oct. 9, 1964 3 Sheets-Sheet 2 INVENTOR -ADALBERT LijHNERT United States Patent Ofifice 3,295,449 Patented Jan. 3, 1967' 8 Claims. oi. 102 70.2

The invention concerns an electrical fuse for projectiles or the like with a piezo-electrical cell as an ignition volt age generator, this cell being under a pressure stress in the discharged phase of the projectile, so that the electrical charge produced thereby serves to ignite the projectile charge. I i In the generation of the pressure affecting the piezoelectrical cell it is already known for an inertia device to be provided in the fuse, this device, in the acceleration of the projectile, pressing against the cell by reason of its mass inertia. The electrical charge caused by this presusre can be used to ignite the projectile charge via electrodes provided on the cell. It is also known for the pressure to be generated on the piezo-electn'cal cell by exposing it to the pressure of the discharge gases or driving gases of the projectile, for example by the insertion of a diaphragm.

The charge produced in the piezo-electrical cell is dependent, apart from the material, on the duration, for a short or longer period, of the pressure. In various projectiles with different discharge accelerations, the pressure affecting the cell and consequently also the charge produced in the cell is therefore different. These knOWn ignition devices consequently do not work safely and perfectly under all conditions.

One of the objects of the invention is to produce a fuse provided with a piezo-electrical cell, in which the charge generated is largely independent of the type of projectile,

.in particular of its discharge acceleration.

A further object of the invention is to increase the charge generated in the piezo-electrical cell as opposed means of a trigger device which becomes effective during the discharge phase of the projectile, by which means the piezo-electrical cell is struck indirectly by a shock wave because of the released energy. The cell is therefore not subjected to a pressure lasting for a short or longer time, but is suddenly traversed by a shock wave, by which a considerable increase of the charge is obtained. The size of this charge is thereby to a large extent independent of the acceleration of the projectile so that the ignition voltage generator operates in a reliable manner even with low accelerations.

According to one embodiment of the invention, there can b provided as the energy carrier and a stressed spring which is attached to a hammer or the like which, on actuation of the trigger device during the discharge phase of the projectile, is accelerated by the relaxing spring and strikes against the piezo-electrical cell or against a baffle plate provided in front of the cell.

, According to a further embodiment of the invention, a detonator can be provided as energy carrier, this detonator being ignited by means of a firing pin actuated on discharge. The pressure or detonating wave caused thereby is led to a piezo-electrical cell provided between a baflle plate and an abutment, and produces in it a shock wave.

In the accompanying drawings, which show, by way of example, particular embodiments constructed in accordance with the invention,

FIGURE 1 is a cross-section, on the line I-I in FIG- URE 2, through a fuse provided with a piezo-electrical cell with a stressed spring as energy carrier,

FIGURE 2 is a section on the line IIII in FIG- URE 1,

FIGURE 3 is a section, corresponding to a section on the line IIIIII in FIGURE 1, through a modified construction of the fuse illustrated in FIGURE 1,

FIGURE 4 is a longitudinal section through a variant of the fuse illustrated in FIGURES l to 3,

FIGURE 5 represents the fuse shown in FIGURE 4 in a released condition,

FIGURE 6 shows a piezo-electrical ignition voltage generator with a detonator as energy carrier.

In the type of construction illustrated in FIGURES 1 and 2 of the said drawings a cylindrical fuse housing made of, for example, aluminum, is indicated by 1. In a block of insulating material 2, which is screwed to a base 9 of the fuse by a screw 8, a piezo-electrical cell 5 is provided between an abutment 3 and a baffie plate 4. A cylindrical stud 6 of the bafile plate 4 protrudes into an aperture in a holding bracket 7 screwed to the fuse base 9, through which bracket the parts 3, 4, 5 are held in the block of insulating material 2. One of the pole-s of the cell 5 is thereby grounded via the baffle plate 4, the stud 6 and the bracket 7.

A pin 10 is inserted into the fuse base 9, and an arm 11 provided with a hammer 12 is pivoted on this pin. One arm 14 of an inertia device 13 rests from below against a pin 15 fixed to the arm 11 (FIGURE 2) and locks the arm 11 in the initial position illustrated, whereby a coil spring 16 provided coaxially on the pin 10 is kept stressed, said stressed spring 16 constituting an energy carrier. The inertia device 13 has two apertures 17 and 18 provided coaxially to one another, the inner aperture 17 containing a guide pin 20 fixed to the base plate 9 and to a cover plate 19. In the outer aperture 18, which is designed as a blind hole, a spring 21 is provided which is supported against the fuse base 9.

To ignite the projectile charge, an electrically ignita'ble detonator 79 is provided which is screwed into a a bore 27 in a detonator carrier 24 which is made of insulating material and is pivoted around a flanged bolt 23 secured to the base 9. Two conductor strips 25 and 26 provided on the top and bottom of the detonator carrier 24 lead to the detonator 79. The strip 25 is connected to the jacket of the detonator 79, and the strip 26 has, at its end, a firing pin 28 provided centrally in the bore 27. The strips 25 and 26 have portions which are presented laterally of the detonator carrier 24 and are designed as contacts 25' or 26'. Further, a wire 29 is soldered to a solder tag on the strip 25, this wire leading to an impact switch 80, which is shown only diagrammatically.

The detonator carrier 24 is provided in the recess of a second block of insulating material 30 and is held in its neutral position by a second arm 33 of the inertia device 13 against the force of a spring 32 surrounding the bolt 23 and engaging with a pin 31. A conductive strip 34 is provided on the block of insulating material 30, this strip possessing two contacts 35 and 36 which are co-ordinated with contacts 25' and 26'. A conducting wire 37 leads from a solder tag 76 on the strip 34 to the metal abutment 3 so that the non-grounded pole of the piezo-electrical cell 5 is connected with strip 34. Between the bracket 7 and the solder tap 76 a diode 38 is connected, whose function is to short circuit the charge of a predetermined polarity of the cell 5. A laminated spring 39 (FIG- URE 2) is soldered to the bottom of the detonator carrier 24, the end of this spring lying upon the fuse base 9 and locating in a recess 40 (FIGURE 1) of the base 9 when the detonator carrier 24 is pivoted inwards, so that an oscillation of the detonator carrier 24 around its switched-on position is avoided.

When the projectile is discharged the fuse is accelerated in the direction shown by an arrow in FIGURE 2, so that the inertia device 13, because of its mass inertia, moves against the fuse base 9 against the force of the spring 21. Its lower arm 14 thereby releases the arm 11, which is pivoted clockwise by the spring 16 until the hammer 12 strikes against the stud 6 of the bafile plate 4, whereby a shock wave passes through the cell 5. The electrical charge arising during the loading phase of the cell is thereby short circuited by the appropriately-poled diode 38, and the charge arising through the discharge of cell 5 remains stored in cell 5 for the time being as diode 38 is lying in the blocking direction for this charge. When the discharge acceleration has ceased, the spring 21 relaxes and presses the inertia device 13 upwards towards the cover plate 19 so that the arm 33 releases the detonator carrier 24. The detonator carrier 24 is pivoted into the ignition position by the spring 32, the laminated spring 39 coming to rest in the recess 40 of the fuse base 9. At the same time the firing pin 28, via the closing contacts 26' and 36, is connected to that pole of the piezoelectrical cell 5 which is not grounded. On the impact of the projectile, the wire 29, and thereby, via the strip 25, the jacket of the detonator 79, is grounded by means of the impact switch 80, so that the charge stored in the cell 5 can equalise via the detonator 79 and ignite the said detonator 79. The ignition flash is led to the projectile charge through an opening 41 provided in the cover plate 19.

If, through a fault in the impact switch 80, the wire is grounded before the detonator carrier 24 has been pivoted into the ignition position, the piezo-electrical cell 5 is short-circuited via the contacts 25' and 35 which are in this case closed, that is to say both poles of cell 5 are grounded so that the charge of the cell 5 is equalized and no ignition of the detonator follows.

To provide security against unintentional operation of the fuse, a ball 43 which is radially movable is provided in a hole 42 in the fuse housing 1. The ball 43 is pressed into a notch 46 in the inertia device 13 by means of a strap 44 which can be tightened by a fastener 45, so that the inertia device is locked. On inserting the projectile into the barrel the strap fastener 44, 45 is slipped off and the fuse made live, as the ball can move through to the outside and release the inertia device 13.

In the type of construction of the fuse illustrated in FIGURE 3, those parts of the fuse which are the same as in FIGURES 1 and 2 have been provided with the same reference numerals. In this case the lower arm 14 of the inertia device 13 lies directly against the hammer 12 and locks the arm 11 in its initial position. In the aperture 17 of the inertia device 13, a guide .pin 47 has been inserted, in this embodiment, this pin having a partly corrugated surface. In a cut-out 48 of the inertia device 13 a plate 49 is provided which has two lugs 50 and 51. Two semi-circular recesses 52 in the plate 49 engage with two shanks 53 of a spring, which is fixed, in a manner not shown, to the inertia device 13. Through the force of the spring shanks 53, the lugs 50, 51 of the plate 49 are pressed against the corrugated surface of the pin 47. The distance between the lugs 50, 51 has been so selected that only one lug at a time can engage with a corrugation of the pin 47, To provide security against unintentional operation of the fuse, the ball 43, in this type of construction, is jammed between a notch 77 in the fuse housing 1 and a bush 78 of soft material, for example aluminium, which is inserted into a hole in the inertia device 13. The inertia device 13 is supported against the fuse base 9 'by means of springs which, for example, engage with its arms 14, 33.

On discharge, the fuse is accelerated leftwards (as viewed in FIGURE 3). The inertia device 13 attempts to move towards the fuse base 9 by reason of its mass inertia, so that the ball 43 is pressed into the inside of the bush 78 and releases the said inertia device 13. In the now-ensuing movement of the inertia body 13, one of the lugs 50, 51 engages in turn with the corrugations of the pin 47 so that the movement of the inertia body and therefore the release of the arm 11 is delayed because of the friction occurring thereby. When the discharge acceleration is relaxed the inertia device moves against the cover plate 19. This movement and therefore the release of the detonator carrier 24 (FIGURE 1) is also delayed in the same manner as described above. The plate 49 thus acts together with the corrugated surface of the pin 47 as a time link.

This fuse can be employed in connection with projectiles which possess a high discharge acceleration. Through the delayed movement of the inertia device 13 and the delayed release of the arm 11 and the detonator carrier, safety is increased on discharge, because the detonator carrier 24 cannot take up its position until the projectile has at least left the barrel.

In the construction shown in FIGURES 4 and 5 an inset of insulating material 54 is provided in a cylindrical fuse housing 22, this inset having a recess for the abutment 3. The baflle plate 4 and the piezo-electrical cell 5 are held together by means of a metal holding device 55 which supports a socket 56 which guides a hammer 57. In the non-released position of the fuse the hammer 57, provided with an inclined face 59, is held by movable balls 60 provided in holes 58 of the socket 56, and the hammer for its part keeps stressed a coil spring 61 which is supported at the one end against the hammer 57 and on the other end against an end support (not shown). By this means the balls 60 are jammed between the inclined face 59 and an axially movable inertia device 62 which surrounds coaxially the socket 56 and the holding device 55. The spring 61 is guided in a guide of insulating material 63 which fixes the socket 56 in its position. The inertia device 62 is supported against the inset 54 by means of a spring 64. The voltage of the piezo-electrical cell 5 can be taken from the baffle plate 4 and from the abutment 3. The abutment 3 and the fuse inset 54 are held by a screw 65; one of the poles of the cell 5 is thus grounded. A foil of insulating material 66 is provided for the insulation of the other pole.

In this construction also a diode (in this case indicated at 38) is in parallel to the cell 5 and short circuits the charge occurring when the cell 5 is loaded. The charge obtained on discharging the cell 5 is preferably stored in the cell 5 itself, serving at the same time as a condenser, and can be used to ignite the projectile charge, for example, via an impact switch.

When discharging the projectile, the inertia device 62 is moved by the discharge acceleration towards the fuse inset 54 against the force of the spring 64. The balls 60 are pressed through the holes 58 by the inclined face 59 of the hammer 57, so releasing the hammer 57. The spring 61 can extend and the hammer 57 strikes against the baffle plate 4 and produce-s an electrical charge in the piezo-electrical cell 5 in the same manner as already described.

In the construction shown in FIGURE 6 a detonator 67 in a fuse housing 68 is provided to produce the shock wave in the piezoelectrical cell 5. The fuse housing, shown at 68, is provided with a screw cap 69 in which a firing pin 7 t is positioned. The firing pin 70 is supported against a cup spring 71 and is centered by means of a guide device 72.

On discharge, the firing pin 70 punctures the detonator 67 causing it to ignite. The pressure and detonating wave caused thereby is led through a duct to the baffle plate 4, whereby the piezo-electrical cell 5 receives a shock wave. The charge in the cell 5 in this case can also be taken from the baifie plate 4 and the abutment 3. In this case parts 3, 4, 5 are fixed in position by a holder 74 of insulating material.

In order for the shock wave to reach the piezo-electrical cell 5 as undamped as possible and so that no reflexes occur between the baffle plate 4 and the cell 5, it is preferable in all the above-described constructions to choose a material for the bafile plate 4 whose sound resistance is about equal to that of the piezo-electrical cell 5.

I claim:

1. An electrical fuse for projectiles which comprises: a piezo-electric cell for generating ignition voltage, an imp-act plate in front of said cell, tensioned spring means, a hammer engaged by said spring means and adapted to be accelerated by said spring means, latch means normally holding said hammer in tensioned position and including ball means, said hammer being so located relative to said plate and cell that in response to said latch means becoming effective, said hammer will impact upon said impact plate arranged in front of said piezo-electric cell and produce an electric charge in said cell, an inclined surface on the front edge of the hammer engaged by said ball means, a first sleeve surrounding the front edge of the hammer having hole means in which the ball means is movable radially of the hammer, a lock sleeve surrounding said first sleeve and holding said ball means in effective position, and a spring supporting said lock sleeve so that inertia forces acting on said lock sleeve at the time of acceleration of said projectile will move said lock sleeve to release said ball means for outward movement in said first sleeve thereby to release said hammer.

2. An electrical fuse for a projectile comprising; a piezo-electrical cell operable upon the application of pressure thereto to develop an ignition voltage for igniting the charge in a projectile in which the fuse is mounted, a hammer element in the fuse moveable to develop pressure on said cell by impact thereon, a first spring biasing said hammer element toward said cell, a trigger arm having one end engaging said hammer element and normally holding the hammer element in ineffective position, an inertia body connected to the other end of said trigger arm, said inertia body being moveable in one direction to move said trigger arm into ineffective position out of engagement with said hammer element thereby to release said hammer element to cause pressure to be developed on said cell thereby, a second spring urging said inertia body in the other direction, and inertia forces acting on said inertia body when the projectile is accelerated during the firing phase thereof urging the said inertia body in the said one direction.

3. A fuse according to claim 2 in which a second trigger arm is attached to said inertia body, a pivoted detonator carrier in said fuse having a detonator thereon and spring biased toward ignition position, said second trigger arm normally holding said detonator carrier in inoperative position, stop means on said hammer element preventing movement of said inertia body in said other direction beyond a predetermined point when said first mentioned trigger arm is in engagement with said hammer element, said second trigger arm being disengageable from said detonator carrier in response to movement of said inertia body in said other direction beyond said predetermined point where said second spring relaxes following the said acceleration of the projectile.

4. A fuse according to claim 3 in which two electrical leads lead from the detonator carried by said detonator carrier, a normally open impact switch on the projectile having one terminal connected to one of said leads and the other terminal connected to one side of said cell and adapted to close upon impact of the projectile, a first contact connected to the other side of said cell, and a second contact on said detonator carrier connected to said other lead and adapted to close on said first contact when the detonator carrier swings into ignition position.

5. A fuse according to claim 4 in which a third contact is provided on said detonator carrier and connected to said one lead, and a fourth contact connected to said other side of said cell and adapted for engagement of said third contact when said carrier is held in inoperative position by said second trigger arm so as to short circuit said cell upon closing of the impact switch if the carrier is in inoperative position.

6. A fuse according to claim 2 in which a stationary corrugated pin is provided on which said inertia body is slidably mounted, a plate carried by the inertia body having a pair of lugs and spring pressed toward the corrugated pin to cause the lugs to engage in the corrugation thereof, said plate being tiltable to step the lugs over the ribs between the corrugations whereby movement of said inertia body is delayed. I

7. A fuse according to claim 2 in which said inertia body has a recess therein, a ball in the recess locking said body against movement in either direction, and a removable strap on the fuse holding the ball in place and removeable to permit movement of the ball to ineffective position.

8. A fuse according to claim 2 in which said inertia body has a recess therein, a bushing of soft material in the recess, a ball in the bushing, a stationary member adjacent the bushing having a second conical recess receiving said ball and thus holding said inertia body stationary, said bushing being deformable when the inertia body is accelerated by the force of the ball engaging the periphery of the conical recess to permit the ball to move into the bushing and disengage from said conical recess and release said inertia body.

References Cited by the Examiner UNITED STATES PATENTS 2,676,273 4/ 1954 Oestreicher. 2,853,012 9/1958 Rotkin et a1. 102 -70.2 2,970,545 2/ 1961 Howe 10270.2 2,991,716 7/1961 Israel et al. 102-70.2 3,175,496 3/1965 Rochat 102--70.2

FOREIGN PATENTS 909,549 10/1962 Great Britain.

SAMUEL FEINBERG, Primary Examiner. BENJAMIN A. BORCHELT, Examiner. W. C. ROCH, Assistant Examiner. 

2. AN ELECTRICAL FUSE FOR A PROJECTILE COMPRISING; A PIEZO-ELECTRICAL CELL OPERABLE UPON THE APPLICATION OF PRESSURE THERETO TO DEVELOP AN IGNITION VOLTAGE FOR IGNITING THE CHARGE IN A PROJECTILE IN WHICH THE FUSE IS MOUNTED, A HAMMER ELEMENT IN THE FUSE MOVEABLE TO DEVELOP PRESSURE ON SAID CELL BY IMPACT THEREON, A FIRST SPRING BIASING SAID HAMMER ELEMENT TOWARD SAID CELL, A TRIGGER ARM HAVING ONE END ENGAGING SAID HAMMER ELEMENT AND NORMALLY HOLDING THE HAMMER ELEMENT IN INEFFECTIVE POSITION, AN INERTIA BODY CONNECTED TO THE OTHER END OF SAID TRIGGER ARM, SAID INERTIA BODY BEING MOVEABLE IN ONE DIRECTION TO MOVE SAID TRIGGER ARM INTO INEFFECTIVE POSITION OUT OF ENGAGEMENT WITH SAID HAMMER ELEMENT THEREBY TO RELEASE SAID HAMMER ELEMENT TO CAUSE PRESSURE TO BE DEVELOPED ON SAID CELL THEREBY, A SECOND SPRING URGING SAID INERTIA BODY IN THE OTHER DIRECTION, AND INERTIA FORCES ACTING ON SAID INERTIA BODY WHEN THE PROJECTILE IS ACCELERATED DURING THE FIRING PHASE THEREOF URGING THE SAID INERTIA BODY IN THE SAID ONE DIRECTION. 